Rapid mountain snowmelt; above-average May runoff

Photo By Eileen Williamson | The Elements of Runoff - Mountain snow water equivalent for Upper Missouri River Basin...... read more read more

Photo By Eileen Williamson | The Elements of Runoff - Mountain snow water equivalent for Upper Missouri River Basin Runoff - Mountain snow begins to accumulate in October, peaks in April and snowmelt is usually complete by mid-July. The June 1 runoff forecast is 26.8 million acre feet. Warm temperatures led to a quick melt of the mountain snowpack. The rapid melting combined with precipitation in the western half of the Basin resulted in above-average inflow into the reservoir system.  see less | View Image Page

OMAHA, NE, UNITED STATES

06.06.2023

Story by Eileen Williamson 

U.S. Army Corps of Engineers, Northwestern Division

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OMAHA, Neb. – Warm temperatures in the mountainous region of the upper Missouri River Basin has led to a quick melt of the mountain snowpack. The rapid melting combined with precipitation in the western half of the Basin resulted in above-average inflow into the reservoir system.
May runoff for the Basin above Sioux City, Iowa was 4.9 million acre-feet, 144% of average.
"The warm temperatures in the northern Rockies has melted the snow earlier than is typical,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division.
“With much of the mountain snowpack already melted, the Basin will need additional rainfall to continue the trend of above-average runoff.”
The annual runoff forecast above Sioux City, IA is 26.8 MAF, 104% of average, and about the same as last month’s forecast. While portions of the Basin received above-normal rainfall, precipitation was below normal over most of the Basin during May.
“The precipitation during the month of May provided some relief to the western half of the Basin, but the drought continues to worsen in other areas. There is some level of drought present in every state with the worst conditions in Nebraska and Kansas,” said Remus.
System storage is currently 52.6 MAF, 3.5 MAF below the top of the carryover multiple use zone. During May, System storage increased 2.5 MAF.
"The June 1 reservoir studies indicate navigation flow support for the second half of the navigation season, based on the forecasted July 1 System storage check, will be increased to 2,500 cubic feet per second below full service,” said Remus. Basin and river conditions continue to be monitored and System regulation will be adjusted based on the most up-to-date information.
“As we enter into the summer months, we will continue to serve all Congressionally authorized purposes while dealing with the on-going drought,” said Remus.

Mountain Snowpack:
Mountain snowpack in the upper Missouri River Basin has melted quickly due to warmer-than-normal temperatures during the spring and early summer. On June 1, only 16% of the annual peak remains in the reach above Fort Peck Dam, and 13% of the annual peak remains in the Fort Peck Dam to Garrison Dam reach. The mountain snowpack peaked in the reach above Fort Peck on April 24 at 117% of average, while the mountain snowpack in the Fort Peck to Garrison reach peaked on April 6 at 109% of average. Mountain snowpack normally peaks near April 17. The mountain snowpack graphics can be viewed at: http://go.usa.gov/xARQC.

Navigation:
Gavins Point Dam releases will provide minimum-service navigation flow support at all four target locations (Sioux City, Omaha, Nebraska City, and Kansas City) through the first half of the navigation season which ends on July 1. Flow targets may be missed to conserve water if there is no commercial navigation in a given reach. Minimum-service flow targets range from 25,000 cubic feet-per-second at Sioux City, Iowa to 35,000 cfs at Kansas City, Missouri. Flow support for the second half of the navigation season, as well as the navigation season length, will be based on the actual System storage on July 1. The current forecast indicates that flow support 2,500 cfs below full service will be provided for the second half of the navigation season and flow support may be provided for the entire navigation season ending Dec. 1 at the mouth of the Missouri River.

Monthly Water Management Conference Calls
Water management calls include an update from the National Weather Service’s Missouri Basin River Forecast Center, and an update on the Missouri River mainstem reservoir system operations. The next call will be held Thursday, June 8. Due to continuing drought conditions, a call will be held July 13. All calls are recorded in their entirety and are available to the public on our website at https://go.usa.gov/xARQv.

Reservoir Forecasts:
Gavins Point Dam
o Average releases past month – 19,400 cfs
o Current release rate – 20,000 cfs
o Forecast release rate – 20,500 cfs
o End-of-May reservoir level – 1206.6 feet
o Forecast end-of-June reservoir level – 1206.1 feet
o Notes: The Gavins Point release will be adjusted to provide minimum-service navigation flow support on the lower Missouri River.

Fort Randall Dam
o Average releases past month – 16,700 cfs
o End-of-May reservoir level – 1357.0 feet
o Forecast end-of-June reservoir level – 1355.3 feet
o Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point and to back up Gavins Point releases.

Big Bend Dam
o Average releases past month – 18,300 cfs
o Forecast average release rate – 14,200 cfs
o Forecast reservoir level – 1420.4 feet

Oahe Dam
o Average releases past month – 17,800 cfs
o Forecast average release rate – 14,100 cfs
o End-of-May reservoir level – 1602.0 feet (up 2.2 feet from April 30)
o Forecast end-of-June reservoir level – 1605.2 feet

Garrison Dam
o Average releases past month – 19,300 cfs
o Current release rate – 22,000 cfs
o Forecast release rate – 22,000 cfs
o End-of-May reservoir level – 1832.8 feet (up 3.6 feet from April 30)
o Forecast end-of-June reservoir level – 1835.9 feet
o Notes – Releases will be maintained at 22,000 cfs through mid-September.

Fort Peck Dam
o Average releases past month – 7,300 cfs
o Current release rate – 8,000 cfs
o Forecast average release rate – 9,000 cfs
o End-of-May reservoir level – 2225.8 feet (up 3.9 feet from April 30)
o Forecast end-of-June reservoir level – 2228.1 feet
o Notes: Releases will be maintained at 9,000 cfs through mid-September.

The forecast reservoir releases and elevations discussed above are not definitive. Additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.

Hydropower:
The six mainstem power plants generated 633 million kWh of electricity in May. Typical energy generation for May is 793 million kWh. The power plants are expected to generate 7.6 billion kWh this year, compared to the long-term average of 9.4 billion kWh.
To view the detailed three-week release forecast for the mainstem dams, go to https://go.usa.gov/xARQB.

The Missouri Basin Web App provides links to these reports and others that are updated more frequently. http://go.usa.gov/xE6fC